Pine Cove in Idyllwild in Riverside County, California — The American West (Pacific Coastal)

Speed-of-Light Experiment

Photographed by Craig Baker, September 14, 2023

1. Speed-of-Light Experiment Marker

Inscription. From this location instruments reflected light in 1926 to Mount Wilson, 82 miles northwest. The work was one of a series of experiments conducted by Nobel Prize-winning scientist Dr. Albert A. Michelson to refine the value of the speed of light. Although smoke generated in the valley below prevented measurements from being taken, the experiment encouraged Dr. Michelson to devise more accurate means of measuring the speed of light.

Erected 1989 by San Jacinto Mountain residents; E Clampus Vitus; and Riverside County Historical Commission. (Marker Number 26.)

Topics and series. This historical marker is listed in this topic list: Science & Medicine. In addition, it is included in the E Clampus Vitus series list. A significant historical year for this entry is 1926.

Location. 33° 45.552′ N, 116° 44.684′ W. Marker is in Idyllwild, California, in Riverside County. It is in Pine Cove. It is at the intersection of Pine Cove Road and Chickadee Lane, on the right when traveling north on Pine Cove Road. Touch for map. Marker is at or near this postal address: 52610 Pine Cove Rd, Idyllwild CA 92549, United States of America.

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Regionally, this marker is in Greater Los Angeles,

in the Inland Empire,

and in the Peninsular Ranges.

It is also in the American Southwest.

Globally, it is in North America,

on the Ring of Fire,

in the Pacific Rim,

in the Western Hemisphere,

in the Western World,

and in the Anglosphere.

Historically, it finds itself in what was once New Spain

and also Mexico’s Alta California.

Other nearby markers. At least 8 other markers are within 4 miles of this marker, measured as the crow flies: Donaldson Futuro (approx. half a mile away); Idyllwild Campground Pictograph (approx. 1.6 miles away); Camp Emerson (approx. 1.8 miles away); Logging Shaped This Landscape (approx. 1.9 miles away); Hoxie-Vance Cabin (approx. 1.9 miles away); The Idyllwild Monument (approx. 2.1 miles away); Idyllwild Town Hall (approx. 2.2 miles away); Tahquitz Rock History (approx. 3.4 miles away). Touch for a list and map of all markers in Idyllwild.

Regarding Speed-of-Light Experiment. Dr. Michelson was the first American to win a Nobel Prize in a scientific field. He spent more than 50 years studying light. Two concrete foundations

Photographed by Craig Baker, September 14, 2023

2. Speed-of-Light Experiment Marker

The square concrete block is visible in the background at right, between the trees.

at the Pine Cove site, a pyramid and a square block, both of which still remain, supported equipment for the experiment. The foundations are approximately 50 feet apart, with their tops at identical levels. A tube between them held mirrors to reflect the light back to Mt. Wilson, where it was to be measured. The Riverside Historical Commission had placed a marker at the site in 1969. SOURCE: Billy Holcomb Chapter 1069 35th Anniversary Plaque Book by Phillip Holdaway

Related markers. Click here for a list of markers that are related to this marker. — Michelson Speed-of-Light Experiments.

Albert Abraham Michelson image. Click for full size.

courtesy Wikipedia

3. Albert Abraham Michelson

Credits. This page was last revised on May 29, 2026. It was originally submitted on December 19, 2011, by Michael Kindig of Elk Grove, California. This page has been viewed 5,836 times since then and 403 times this year. Last updated on February 13, 2019, by Craig Baker of Sylmar, California. Photos: 1, 2. submitted on September 14, 2023, by Craig Baker of Sylmar, California. 3. submitted on December 22, 2011, by Michael Kindig of Elk Grove, California. • Bill Pfingsten was the editor who published this page.